A variety of primary batteries employ electrolytes with organic solvents such as diethyl carbonate (DEC) and ethylene carbonate (EC). These batteries are often stored for extended periods of time before use. However, the performance of these batteries often drops after this storage. For instance, the capacity of these batteries often decreases after extended storage. Additionally, the pulsing capability of these batteries can drop after storage.
Rechargeable lithium batteries are widely discussed in the literature and are readily commercially available. They typically consist of a positive electrode and a negative electrode spaced by a separator, an electrolyte, a case, and feedthrough pins respectively connected to the electrodes and extending externally of the case. Each electrode is typically formed of a metal substrate that is coated with a mixture of an active material, a binder, and a solvent. In a typical battery design, the electrodes comprise sheets which are rolled together, separated by separator sheets, and then placed in a prismatic case. Positive and/or negative feed through pins (i.e., terminals) are then connected to the respective electrodes and the case is sealed.
The negative electrode is typically formed of a copper substrate carrying graphite as the active material. The positive electrode is typically formed of an aluminum substrate carrying lithium cobalt dioxide as the active material. The electrolyte is most commonly a 1:1 mixture of EC:DEC in a 1.0 M salt solution of LiPF6. The separator is frequently a micro porous membrane made of a polyolefin such as a combination of polyethylene and/or polypropylene.
The demand for lithium batteries has increased enormously in recent years. This increased demand has resulted in ongoing research and development to improve the safety and performance of these batteries. The conventional organic carbonate solvents employed in the electrolytes of many lithium ion batteries are associated with a high degree of volatility, flammability, and chemical reactivity. A variety of electrolytes that include polysiloxane solvents have been developed to address these issues.
Electrolytes that include a polysiloxane solvent typically have a low ionic conductivity that limits their use to applications that do not require high rate performance. Additionally, batteries that include conventional polysiloxane solvents have shown poor cycling performance when used in secondary batteries. As a result, lithium bis-oxalato borate (LiBOB) has been used as the salt in these electrolytes. While LiBOB improves the performance of the batteries, LiBOB is unstable in the presence of water. The amount of moisture in battery electrolytes and/or electrodes can be on the order of several hundred ppm. The presence of this moisture can cause LiBOB to decompose into lithium oxalate (LiHC2O4.H2O) and form a precipitate in the electrolyte. This precipitate tends to increase the internal resistance of electrical devices such as batteries.
Thus there remains a long-felt and unmet need to increase the performance, safety, and storage life of lithium-based batteries and other electrical charge-storing devices.